Wire derailment detecting apparatus of wire saw

ABSTRACT

A microswitch is provided near each end of each grooved roller. The microswitch has a rod-shaped contact shoe, and is operated if a wire derailed from the grooved roller contacts the contact shoe. An operational signal is sent from the microswitch to a control apparatus, and the control apparatus receives the operational signal so as to detect that the wire is derailed.

This is a Divisional application of Ser. No. 08/705,685, filed Aug. 29,1996 now U.S. Pat. No. 5,809,986.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wire derailment detecting apparatusof a wire saw, and more particularly to a wire derailment detectingapparatus of a wire saw which slices a workpiece such as a semiconductoringot into a number of wafers by a running wire.

2. Description of the Related Art

In a wire saw, a wire, which runs at a high speed between a pair of wirereels, is wound on a plurality of grooved rollers to form a wire row.The workpiece is pressed against the wire row supplied withmanufacturing solution including abrasive grains. As a result, theworkpiece can be sliced into a number of wafers by lapping action of theabrasive grains.

In the wire saw, the wire must be prevented from snapping while theworkpiece is being sliced. The wire is snapped mainly because the wireis derailed from the grooved rollers forming the wire row, and becausethe wire is derailed from the guide roller guiding the running wire.

In order to detect whether the wire is derailed, there is a method inthat a pair of the wire reels are electrically insulated from a body ofthe wire saw, and a constant voltage is applied between the wire reels.Then, when a drop in the voltage is detected, then it is determined thatthe wire is derailed. This method is based on the following facts. Thatis, many of the grooved rollers and the guide rollers are made of resinsuch as rubber, polyurethane, polyethylene, or the like. If the wire isnormally wound on the rollers, there is a constant difference in voltagebetween the wire reels. If the wire is derailed, the wire contacts thebody of the wire saw, and the voltage is dropped.

The current manufacturing solution of the wire saw is usually oil-based.The oil-based manufacturing solution is faced with problems in which thesliced wafer cannot be cleansed sufficiently, the user becomes stainedwith the solution, and the environment is polluted. Therefore, awater-based manufacturing solution has been recently developed to anextent that it can be put to practical use.

However, if the conventional method of electrically detecting thederailment is applied to the wire saw performing the slicing by means ofthe water-based manufacturing solution, the manufacturing solutionconducts electricity. Thus, there are disadvantages in that theoperation is incorrect and the detection is delayed.

SUMMARY OF THE INVENTION

The present invention has been developed under the above-describedcircumstances, and has its object the provision of a wire derailmentdetecting apparatus of a wire saw, which can be applied to a wire sawperforming the slicing by means of the water-based manufacturingsolution.

In order to achieve the above-mentioned object, a wire derailmentdetecting apparatus of a wire saw, in which a wire guided by a pluralityof guide rollers and travelling between a pair of wire reels is wound ona plurality of grooved rollers to form a wire row, and a workpiece ispressed against said wire row to be sliced into a number of wafers,comprises: switch means provided near each end of each of the groovedrollers, and operated to send an operational signal if the wire derailedfrom the grooved roller contacts the switch means; and control means forreceiving the operational signal sent from the switch means so as todetect whether the wire is derailed from the grooved roller.

According to the present invention, when the wire wound on the groovedrollers is derailed from one of the ends of one of the grooved rollers,it contacts the switch means provided near the end of the groovedroller. If the wire contacts the switch means, the switch means isoperated, then the switch means sends the operational signal to thecontrol means. The control means receives the operational signal sentfrom the switch means so as to detect that the wire is derailed from thegrooved roller.

In order to achieve the above-mentioned object, a wire derailmentdetecting apparatus of a wire saw, in which a wire guided by a pluralityof guide rollers and travelling between a pair of wire reels is wound ona plurality of grooved rollers to form a wire row, and a workpiece ispressed against the wire row to be sliced into a number of wafers,comprises: means for measuring the number of rotations of each guideroller of the plurality of guide rollers while the workpiece is beingsliced; and control means for comparing the number of rotations of theguide roller measured by the means for measuring the number ofrotations, and a predetermined reference number of rotations of theguide roller, so as to detect whether the wire is derailed from theguide roller.

According to the present invention, the means for measuring the numberof rotations measures the number of rotations of the guide roller whilethe workpiece is being sliced, and the measurement result is sent to thecontrol means. On the other hand, the control means compares the numberof rotations of the guide roller during the slicing of the workpiece,which is sent from the means for measuring the number of rotations, andthe predetermined reference number of rotations of the guide roller. Inthis case, if the wire is normally wound on the guide roller, the numberof rotations during the slicing of the workpiece, which is measured bythe means for measuring the number of rotations, is substantially equalto the reference number even if the wire is slippery. However, if thewire is derailed from the guider roller, the guide roller does notrotate, so that the number of rotations during the slicing is not equalto the reference number. When the wire is wound on the portion of theguide roller other than the grooved portion, the number of rotationsduring the slicing is less than or more than the reference number.Therefore, when the difference between the number of rotations duringthe slicing of the workpiece and the reference number is out of apermissible range, the control means determines that the wire isderailed from the guide roller.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of this invention, as well as other objects and advantagesthereof, will be explained in the following with reference to theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures and wherein:

FIG. 1 is a view illustrating the structure of the whole wire saw;

FIG. 2 is a side view illustrating grooved rollers;

FIG. 3 is a sectional view taken along line 3--3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4--4 in FIG. 3;

FIG. 5 is a side sectional view illustrating a wire derailment detectingapparatus; and

FIG. 6 is a sectional view taken along line 6--6 in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, an explanation will be given about the structure of a wire saw.FIG. 1 is a view illustrating the structure of the whole wire saw 10.

As shown in FIG. 1, a wire 14 wound on one wire reel 12 is wound onthree grooved rollers 22A, 22B, and 22C, which are arranged in such amanner to form a triangle, via a wire guiding apparatus 16A, a pluralityof guide rollers 18,18, . . . , and a dancer roller 20A. The wire 14forms a wire row 24. The wire 14 forming the wire row 24 is wound up bythe other wire reel 26 via a plurality of guide rollers 18,18, . . . , adancer roller 20B, and a wire guiding apparatus 16B.

The wire guiding apparatuses 16A and 16B guide the wire 14 so that thewire 14 can be reeled out of the wire reels 12 and 26 at a constantpitch, and so that the wire 14 can be wound up by the wire reels 12 and26 at a constant pitch. The guide roller 18 is disposed at apredetermined position of a wire travelling path so as to guide the wire14 running between a pair of the wire reels 12 and 26. Weights 44A and44B of a predetermined weight are hung from the dancer rollers 20A and20B to always apply a constant tension to the traveling wire 14.

Wire cleansing apparatuses 46A and 46B are provided on the wiretravelling path. The wire cleansing apparatuses 46A and 46B eliminatemanufacturing solution 40 adhered to the circumference of the wire 14 bypassing the travelling wire 14 through the cleansing solution.

Motors 28 and 30, which are able to rotate in the forward and backwarddirections, connect to a pair of the wire reels 12 and 26, respectively.The motors 28 and 30 are driven so that the wire 14 can travel back andforth between a pair of the wire reels 12 and 26. A motor 32, which isable to rotate in the forward and backward directions, connects to thegrooved roller 22A. The motor 32 is controlled to be drivensynchronously with the motors 28 and 30.

The wire row 24 is supplied with slurry 40 (manufacturing solution)stored in a slurry storage tank 38, via slurry supplying nozzles 42A and42B. The slurry 40 supplied to the wire row 24 includes abrasive grains(ordinarily, abrasive grains of approximately GC #600-#1000 are used). Aworkpiece is sliced by lapping action of the abrasive grains.

A work feed table 48, which is driven by a work feed motor 50 to move upand down, is disposed below the wire row 24. A semiconductor ingot 54 asthe workpiece is fixed to the work feed table 48 via an ingot mountingblock 56 and a slice base mounting beam 58. The work feed table 48 islifted toward the wire row 24 so that the semiconductor ingot 54 can bepressed against the wire row 24 running at a high speed and can besliced into a number of wafers.

Next, an explanation will be given about the wire derailment detectingapparatus according to the present invention. In order to detect whetherthe wire 14 is derailed, there are two cases when the derailment of thewire 14 from the grooved roller 22A, 22B or 22C is detected, and whenthe derailment of the wire 14 from the guide roller 18 is detected.First, an explanation will be given about the case when the derailmentof the wire 14 from the grooved roller 22A, 22B, or 22C is detected.

FIG. 2 is a side view illustrating the grooved rollers 22A, 22B, and22C. FIG. 3 is a sectional view illustrating along line 3--3 in FIG. 2.

As shown in FIGS. 2 and 3, the grooved rollers 22A, 22B and 22C areconstructed in such a manner that spindles 62A, 62B and 62C are engagedwith the center of rollers 60A, 60B, and 60C made of polyurethane. Manygrooves are formed on the outer circumference of the rollers 60A, 60Band 60C at a constant pitch. The wire 14 is wound on the groovessequentially so as to form the wire row 24.

The grooved rollers 22A, 22B and 22C are rotatably held by a pair ofholding plates 64 and 64, which both ends are fixed to a body frame (notshown) of the wire saw, via bearings 66A, 66A, 66B, 66B, 66C, and 66C.

Microswitches 68A, 68A, 68B, 68B, 68C, and 68C are provided on a pair ofthe holding plates 64 and 64 near the holding parts of the groovedrollers 22A, 22B and 22C.

As shown in FIG. 4, the microswitch 68B is attached to the holding plate64 via a bracket 70B. The microswitch 68B is provided with a rod-shapedcontact shoe 72B. If the wire 14 contacts the contact shoe 72B, themicroswitch 68B is operated.

Therefore, the microswitch 68B is attached to the holding plate 64 sothat the derailed wire 14 can contact the contact shoe 72B without failwhen the wire 14 is derailed from the grooved roller 22B.

Other microswitches 68A and 68C are constructed in the same manner. Whenthe wire 14 is derailed from the grooved roller 22A, 22B or 22C, themicroswitch 68B, 68B and 68C are attached to the holding plate 64 sothat the derailed wire 14 can contact the contact shoe 72A, 72B, or 72C.

When the microswitch 68A, 68B or 68C is operated, it sends anoperational signal to a control apparatus (not shown). When the controlapparatus receives the operational signal, it determines from whichroller of the grooved rollers 22A, 22B, and 22C the wire is derailed. Atthe same time, the control apparatus stops the motors 28, 30, and 32 ofthe wire reels 12 and 26, and the grooved roller 22A, and stops the workfeed motor 50.

The wire derailment detecting apparatus constructed in theabove-mentioned manner detects whether the wire 14 is derailed from thegrooved roller 22A, 22B, or 22C in the following way.

As shown in FIG. 1, the wire 14 reeled out of one wire reel 12 is woundup by the other wire reel 26 via the wire guiding apparatus 16A→ theguide roller 18→ the dancer roller 20A→ the three grooved rollers 22A,22B, and 22C→ the guide roller 18→ the dancer roller 20B→ the wireguiding apparatus 16B.

The wire 14 is wound on a number of grooves on the outer circumferenceof the rollers 60A, 60B, and 60C, so that the wire row 24 is formed atthe three grooved rollers 22A, 22B and 22C.

However, if the user makes a mistake in winding the wire 14, or if sometrouble occurs, the wire 14 is derailed from the roller 60A, 60B, or60C.

As shown in FIG. 4, when the wire 14 is derailed from, for example, anend of the roller 60B, the derailed wire 14 contacts the contact shoe72B of the microswitch 68B provided at the end of the roller 60B. Whenthe wire 14 contacts the contact shoe 72B, the microswitch 68B isoperated and sends the operational signal to the control apparatus.

On the other hand, when the control apparatus receives the operationalsignal sent from the microswitch 68B, it determines that the wire 14 isderailed from the grooved roller 22B. At the same time, the controlapparatus stops driving the wire saw 10.

As described above, the wire derailment detecting apparatus of the wiresaw in this embodiment detects that the derailed wire 14 contacting themicroswitch 68A, 68B, or 68C in order to determine that the wire 14 isderailed. Therefore, even if the wire saw performs the slicing by meansof water-based slurry, there is no problem of incorrect operation,unlike the conventional method of electrically detecting the derailment.Moreover, the derailment of the wire 14 can be instantaneously detectedwithout fail.

In the wire derailment detecting apparatus in this embodiment, themicroswitches 68A, 68B, and 68C are provided at both ends of each of thegrooved rollers 22A, 22B, and 22C. As a result, it can be determinedfrom which roller of the three grooved rollers 22A, 22B, and 22C thewire 14 is derailed.

Incidentally, in this embodiment, the microswitches 68A, 68B, and 68Care provided near both end of each of the grooved rollers 22A, 22B, and22C. However, the microswitches 68A, 68B, and 68C may be provided at anyposition, if the wire 14 is derailed from the grooved roller 22A, 22B,or 22C will contact the contact shoe 72A, 72B, or 72C without fail. Forexample, the microswitches 68A, 68B, and 68C may be provided halfwaybetween the rollers 22A and 22B, 22B and 22C, and 22C and 22A.

The detecting devices are not restricted to the microswitches 68A, 68B,and 68C. Any switch will do if it is operation when the derailed wire 14contacts it. For example, a close switch or a limit switch can be used.Moreover, a contact detecting sensor may be used instead of the switch.

Furthermore, the wire derailment detecting apparatus in this embodimentmay be applied to not only the wire saw performing the slicing by meansof the water-based slurry, but also a wire saw performing the slicing bymeans of oil-based slurry.

Next, an explanation will be given about the case when the derailment ofthe wire from the guide roller is detected in the above-described wiresaw.

FIG. 5 is a side sectional view illustrating the structure of the wirederailment detecting apparatus when the derailment of the wire from theguide roller is detected.

The guide roller 18 is toroidal and made of resin material such asrubber, plastic, or the like. A V-shaped groove 18A is formed on theouter circumference of the guide roller 18. The guide roller 18 isrotatably held by a bearing unit 162 provided at a body frame 164 of thewire saw.

The bearing unit 162 is composed of a shaft 166, which is fixed to thebody frame 164 of the wire saw, and a rotational axis 168, which isrotatably held at the tip of the shaft 166 coaxially with the shaft 166.

The shaft 166 is fixed to the body frame 164 in such a manner that amale screw 166A at an end thereof is engaged with a screw hole 164Aformed at the body frame 164 of the wire saw.

The rotational axis 168 is shaped like a cylinder, and its outsidediameter is substantially equal to an inside diameter of the guideroller 18. A flange 170 is formed at an end of the rotational axis 168.The rotational axis 168 is rotatably held at the tip of the shaft 166via the bearings 172 and 172, and an aperture at the tip of therotational axis 168 is sealed by a cap 174.

As shown in FIG. 6, measurement holes 176, 176, . . . are punched atregular intervals at ten positions near an outer edge at the back sideof the flange 170 formed at the rotational axis 168.

On the other hand, a close switch 178 is provided at a position of thebody frame 164 of the wire saw, where the measurement holes 176 pass.The close switch 178 is operated when the measurement hole 176 passes,and sends an operational signal to a controller 180.

The controller 180 counts the operational signals sent from the closeswitch 178 and determines whether the wire 14 is derailed according tothe counted number in the following way.

First, suppose that the wire 14 is normally wound on the guide roller18. The number N₀ of operation of the close switch 178 counted by thecontroller 180 for a unit time T is ##EQU1## where L is the length inwhich the wire 14 travels for the unit time T and D is the diameter ofthe groove 18A on the guide roller 18. The number N₀ is the referencenumber of operation of the close switch 178, which is entered into thecontroller 180.

On the other hand, if the wire 14 is completely derailed from the guideroller 18, the guide roller 18 does not rotate, so that the close switch178 is not operated. Therefore, the controller 180 does not count theoperational signals.

In some cases, the wire 14 is derailed from the groove 18A on the guideroller 18 and enters a space between the guide roller 18 and the flange170, and then the wire 14 is engaged with the outer circumference of therotational axis 168. In this case, the guide roller 18 rotates, and thenumber N₁ of operation of the close switch 178 counted by the controller180 for the unit time T is ##EQU2## where d is the outside diameter ofthe rotational axis 168. As described above, the number N₀ of operationof the close switch 178, which is counted by the controller 180 when thewire 14 is normally wound on the guide roller 18, is different from thenumber N₁ of operation of the close switch 178, which is counted by thecontroller 180 when the wire 14 is derailed from the guide roller 18.

The controller 180 counts the operational signals sent from the closeswitch 178 while the wire saw 10 is working, for the unit time T. Then,the controller 180 calculates the difference between the actual number Xof operation of the close switch 178 and the reference number N₀.

If the wire 14 is normally wound on the groove 18A on the guide roller18, the actual number X of the operation is equal to the referencenumber N₀.

However, even if the wire 14 is normally wound on the groove 18A on theguide roller 18, the actual number X of the operation is not alwaysequal to the reference number No. This discrepancy results from the slipof the wire 14, the thinning of the abraded groove 18A on the guideroller 18, and so forth.

Therefore, if the difference between the actual number X of theoperation and the reference number N₀ is in the predeterminedpermissible range, the controller 180 considers that the wire 14 isnormally wound on the groove 18A on the guide roller 18. If thedifference is not in the permissible range, the controller 180determines that the wire 14 is derailed, and stops the wire saw 10 aftera warning. At the same time, the controller 180 determines from whichguide roller the wire 14 is derailed.

As described above, the wire derailment detecting apparatus of the wiresaw in this embodiment detects the number of rotations of the guideroller 18, and according to the number determines whether the wire 14 isderailed. Therefore, even if the wire saw performs the slicing by meansof the water-based slurry, there is no problem of incorrect operation,unlike the conventional method of electrically detecting the derailment.Moreover, the derailment of the wire can be instantaneously detectedwithout fail.

Furthermore, the number of rotations of each of the guide rollers 18 isdetected so that from which guide roller 18 the wire 14 is derailed canbe detected.

Incidentally, the means for measuring the number of rotations of theguide roller 18 is restricted to the close switch 178 and themeasurement hole 176 in this embodiment. A tachometer, an encoder, apulse generator, or the like can be employed.

As has been described above, according to the present invention, theswitches, which are operated when the derailed wire contacts thereof,are provided so that the control apparatus stops the running wireaccording to the operation of the switches. Therefore, there is noproblem of incorrect operation, unlike the conventional method ofelectrically detecting the derailment, and the wire can be preventedfrom snapping without fail.

Moreover, the number of rotations of the guide roller during the slicingis compared with the predetermined reference number of rotations duringthe normal slicing, so that it is determined whether the wire isderailed. When the wire is derailed, the wire is made to stop moving.Therefore, there is no problem of incorrect operation, unlike theconventional method of electrically detecting the wire derailment, andthe wire can be prevented from snapping without fail.

Incidentally, the microswitch having the contact shoe as described abovemay be provided near each the guide roller in order to detect the wirederailment.

It should be understood, however, that there is no intention to limitthe invention to the specific forms disclosed, but on the contrary, theinvention is to cover all modifications, alternate constructions andequivalents falling within the spirit and scope of the invention asexpressed in the appended claims.

I claim:
 1. In a wire saw, in which a wire guided by a plurality ofguide rollers and travelling between a pair of wire reels is wound on aplurality of grooved rollers to form a wire row, and a workpiece ispressed against said wire row to be sliced into a number of wafers, awire derailment detecting apparatus comprising:means for measuring thenumber of rotations of each guide roller of said plurality of guiderollers while said workpiece is being sliced; and control means forcomparing said number of rotations of each guide roller measured by saidmeans for measuring the number of rotations, and a predeterminedreference number of rotations of each guide roller, so as to detectwhether said wire is derailed from at least one of said guide rollers.2. The wire derailment detecting apparatus of the wire saw according toclaim 1, wherein said control means stops said wire when detecting thatsaid wire is derailed from at least one of said guide rollers.
 3. Thewire derailment detecting apparatus of the wire saw according to claim1, wherein said control means warns when detecting that said wire isderailed from at least one of said guide rollers.
 4. The wire derailmentdetecting apparatus of the wire saw according to claim 1, wherein saidcontrol means determines from which guide roller of said plurality ofguide rollers said wire is derailed, by detecting the number ofrotations of each guide roller of said plurality of guide rollers andcomparing said number of rotations and said reference number ofrotations.
 5. The wire derailment detecting apparatus of the wire sawaccording to claim 1, wherein measurement holes are formed on an endface of each guide roller, said measurement holes being arranged on acircle concentric with said end face of said guide roller at a constantpitch; and wherein said means for measuring the number of rotations is aclose switch, said close switch being operated when each of saidmeasurement holes passes, the number of times said close switch isoperated being counted by said control means so that said number ofrotations of said guide roller is detected.